Try looking for an avian vet or a vet that sees farm animals. Also, if you have a vet for other pets, I'd talk to them. The vet personally or a senior vet tech, not just a receptionist. Call your local extension service office or a university that has a veterinary program. Many of the parasites that would be seen in a chicken's fecal would also be in a dog or cats.
If you do, take samples from several birds and mix them together. That way you have 1 test that is covering a good representation of your flock.